不一定
Written bù yī dìng, said bù yí dìng — 一 is yí before a fourth tone and yì before the others.
Meaning
- not necessarily
- maybe
Example sentence
山不一定是绿色的。
Mountains are not necessarily green.
Characters in 不一定
不 not plus 一定 certainly. It is the negation of the whole phrase rather than of 定, so it means not necessarily rather than definitely not.